Historically, printers have been desktop devices and have thus been large and immobile. Printers have had large capacity ink cartridges requiring seldom replacement. Replacement ink cartridges are typically kept on hand so that when the current ink cartridge is exhausted it can be replaced with little interruption to the printer operation.
Recent developments have seen printers being incorporated into portable telecommunications devices such as mobile telephones. Examples of such applications can be found in the present applicant's co-pending applications listed above. However, with a portable printer, there is a problem that a replacement ink cartridge will not always be at hand if the ink supply is exhausted. To overcome this problem the ink cartridge will be replaced before it is absolutely necessary resulting in a wastage of ink otherwise there will be a risk that the ink supply will run out, rendering the printer useless until a replacement ink cartridge is found.